linux/drivers/char
Nils Carlson 273ef9509b drivers/char/hpet.c: fix periodic-emulation for delayed interrupts
When interrupts are delayed due to interrupt masking or due to other
interrupts being serviced the HPET periodic-emuation would fail.  This
happened because given an interval t and a time for the current interrupt
m we would compute the next time as t + m.  This works until we are
delayed for > t, in which case we would be writing a new value which is in
fact in the past.

This can be solved by computing the next time instead as (k * t) + m where
k is large enough to be in the future.  The exact computation of k is
described in a comment to the code.

More detail:

Assuming an interval of 5 between each expected interrupt we have a normal
case of

t0: interrupt, read t0 from comparator, set next interrupt t0 + 5
t5: interrupt, read t5 from comparator, set next interrupt t5 + 5
t10: interrupt, read t10 from comparator, set next interrupt t10 + 5
...

So, what happens when the interrupt is serviced too late?

t0: interrupt, read t0 from comparator, set next interrupt t0 + 5
t11: delayed interrupt serviced, read t5 from comparator, set next
interrupt t5 + 5, which is in the past!
... counter loops ...
t10: Much much later, get the next interrupt.

This can happen either because we have interrupts masked for too long
(some stupid driver goes on a printk rampage) or just because we are
pushing the limits of the interval (too small a period), or both most
probably.

My solution is to read the main counter as well and set the next interrupt
to occur at the right interval, for example:

t0: interrupt, read t0 from comparator, set next interrupt t0 + 5
t11: delayed interrupt serviced, read t5 from comparator, set next
interrupt t15 as t10 has been missed.
t15: back on track.

Signed-off-by: Nils Carlson <nils.carlson@ericsson.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-06-15 20:04:02 -07:00
..
agp agp/uninorth: Fix lockups with radeon KMS and >1x. 2011-05-22 20:23:09 +10:00
hw_random Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2011-05-20 17:24:14 -07:00
ipmi ipmi: convert to seq_file interface 2011-05-26 17:12:37 -07:00
mwave Fix common misspellings 2011-03-31 11:26:23 -03:00
pcmcia pcmcia: Convert pcmcia_device_id declarations to const 2011-05-06 07:46:22 +02:00
tpm char/tpm: Fix unitialized usage of data buffer 2011-03-29 09:45:34 -07:00
xilinx_hwicap drivercore: revert addition of of_match to struct device 2011-05-18 12:32:23 -06:00
apm-emulation.c apm-emulation: apm_mutex breaks ACK; remove it 2011-05-23 12:50:43 +02:00
applicom.c drivers/char/applicom.c: fix information leak to userland 2010-10-27 18:03:14 -07:00
applicom.h
bfin-otp.c llseek: automatically add .llseek fop 2010-10-15 15:53:27 +02:00
briq_panel.c BKL: remove extraneous #include <smp_lock.h> 2010-11-17 08:59:32 -08:00
bsr.c powerpc/pseries/bsr: Remove redundant initialization of bsr dev_t declaration. 2011-05-04 16:02:40 +10:00
ds1302.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
ds1620.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
dsp56k.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
dtlk.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
efirtc.c
generic_nvram.c drivers: autoconvert trivial BKL users to private mutex 2010-10-05 15:01:04 +02:00
genrtc.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
hangcheck-timer.c Input: sysrq - drop tty argument form handle_sysrq() 2010-08-21 00:34:45 -07:00
hpet.c drivers/char/hpet.c: fix periodic-emulation for delayed interrupts 2011-06-15 20:04:02 -07:00
i8k.c i8k: Integrate with the hwmon subsystem 2011-05-25 20:43:33 +02:00
Kconfig Allow setting of number of raw devices as a module parameter 2011-05-06 17:52:31 -07:00
lp.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
Makefile drivers/char: add MSM smd_pkt driver 2011-03-23 19:46:38 -07:00
mbcs.c drivers: autoconvert trivial BKL users to private mutex 2010-10-05 15:01:04 +02:00
mbcs.h Fix common misspellings 2011-03-31 11:26:23 -03:00
mem.c kmsg: properly support writev to avoid interleaved printk lines fix 2011-04-19 17:00:48 -07:00
misc.c llseek: automatically add .llseek fop 2010-10-15 15:53:27 +02:00
mmtimer.c posix-timers: Cleanup namespace 2011-02-02 15:28:19 +01:00
msm_smd_pkt.c drivers/char: add MSM smd_pkt driver 2011-03-23 19:46:38 -07:00
mspec.c drivers/char/mspec.c: use {k,v}zalloc to allocate memory 2011-05-26 17:12:37 -07:00
nsc_gpio.c
nvram.c drivers: autoconvert trivial BKL users to private mutex 2010-10-05 15:01:04 +02:00
nwbutton.c Fix common misspellings 2011-03-31 11:26:23 -03:00
nwbutton.h
nwflash.c drivers: autoconvert trivial BKL users to private mutex 2010-10-05 15:01:04 +02:00
pc8736x_gpio.c llseek: automatically add .llseek fop 2010-10-15 15:53:27 +02:00
ppdev.c drivers/char/ppdev.c: put gotten port value 2011-05-26 17:12:37 -07:00
ps3flash.c drop unused dentry argument to ->fsync 2010-05-27 22:05:02 -04:00
ramoops.c ramoops: fix types, remove typecasts 2011-01-13 08:03:23 -08:00
random.c Fix common misspellings 2011-03-31 11:26:23 -03:00
raw.c RAW driver: Remove call to kobject_put(). 2011-05-06 17:52:32 -07:00
rtc.c of/device: Replace struct of_device with struct platform_device 2010-08-06 09:25:50 -06:00
scc.h
scx200_gpio.c llseek: automatically add .llseek fop 2010-10-15 15:53:27 +02:00
snsc_event.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
snsc.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
snsc.h headers: kobject.h redux 2011-01-10 08:51:44 -08:00
sonypi.c Fix common misspellings 2011-03-31 11:26:23 -03:00
tb0219.c llseek: automatically add .llseek fop 2010-10-15 15:53:27 +02:00
tlclk.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
toshiba.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
ttyprintk.c tty: now phase out the ioctl file pointer for good 2011-02-17 11:59:56 -08:00
uv_mmtimer.c BKL: remove extraneous #include <smp_lock.h> 2010-11-17 08:59:32 -08:00
viotape.c Merge branch 'llseek' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/bkl 2010-10-22 10:52:56 -07:00
virtio_console.c virtio console: don't manually set or finalize VIRTIO_CONSOLE_F_MULTIPORT. 2011-05-30 11:14:13 +09:30